It has been well established in the art that variable speed and continuously variable transmissions have significant utility and for this reason, the prior art is replete with a great number of innovations in this area wherein even most modern designs are still based on generic devices and configurations devised many decades ago.
Current limitations of use of such devices is generally linked with relatively low power density and efficiency compared with conventional multi-speed gear boxes.
Advantageously a frictional gear continuously variable transmission can offer low noise, smooth operation and speed transition and the possibility of being utilized for a vast scope of applications ranging from micro or nano-mechanical devices where saving of microwatts of power can significantly prolong its autonomous life and to variable speed power generation or power transfer in amounts measured in megawatts.
Many existing systems share a common limitation of their designs where neglecting the negative effect of spin at the contract points of rotating bodies drastically reduces available traction leading to unnecessary elevated slip of traction surface relative to each other and finally leading to waste of available energy converted into heat. Elevated heat in turn requires higher circulation of lubrication fluid, larger heat exchangers and pumps, causing therefore increased complexity and cost for such systems and reducing the overall efficiency even further.
At the same time, many existing devices also fail to ensure a simple “up” and “down” scalability, generally due to the complexity of their controlling, clamping and speed variation systems.
Another common disadvantage of existing toroidal systems is that input and output shafts rotational directions differ, which in many instances complicates retrofit installations in continuously variable transmissions for existing motor vehicles and electric generators.
Turning to prior art and, as an example, Forster et al., in U.S. Pat. No. 2,271,688, issued Feb. 3, 1942, discloses a variable speed friction drive. The innovation in the document relates to the novel spring biased ball assembly which is used as a transmitting medium between a drive member and a driven member. The ball assembly provides the balls in contacting relation along the line forming an acute angle with respect to a line perpendicular to the surface of the disc-shaped driving member. A spring is provided which biases one race containing the balls with respect to the other so as to tend to decrease the angle and thus maintain continuous driving engagement between the driving member, balls and driven member. This provided a significant improvement in the variable speed friction drive arrangements.
In U.S. Pat. No. 1,093,922, issued Apr. 21, 1914 to Dieterich, there is disclosed a power transmission apparatus. The transmission apparatus converts high speed power to low speed power and vice versa and broadly provides the combination of a driving member, a driven member together with a plurality of sets of co-acting rollers for transmitting motion from one to the other. The sets of rollers are adapted to transmit power interposed between coaxial or eccentrically disposed member relative to a shaft of the device.
Jacobsen, in U.S. Pat. No. 1,775,201, issued Sep. 9, 1930, provides for a change of speed friction drive. In this arrangement, the patentee provided a novel arrangement for a change of speed friction drive power transmission which combined an angular raceway, a second angular raceway rolling friction members interposed between the raceways having variable contract therewith and means of forming an axis, to and for supporting the raceway's concentrically and substantially in the same plane and for relative rotation about the axis and including an input shaft held against axial displacement. The shaft is rotatable about the axis and connected to and for rotating these second mentioned raceway to communicate power to the mechanism. The combination further included an output shaft which was held against any axial displacement and which was rotatable about the axis connected to the first angular raceway and rotated thereby.
U.S. Pat. No. 1,870,421, issued Aug. 9, 1932, to Prout provides for a system of friction gearing. In the Patent, the patentee teaches a simple mechanism for transmitting power which is capable of operating quietly and smoothly at a high rate of speed without any possibility of a slippage when presented with a heavy load. In the arrangement, the system provides a drive shaft, a driven shaft parallel thereto, friction wheels having beveled friction surfaces with the friction wheels on the drive shaft comprising different diameters than friction wheels on the driven shaft and intermediate friction wheels having beveled surfaces of different diameters and face angles for engaging friction wheels on the driving and driven shafts. In the embodiment shown, the intermediate friction wheels are mounted for floatable movement above and between the driving and driven friction wheels and driveable in a direction to be drawn into closer contact with the wheels by the tangential forces being transmitted.
In U.S. Pat. No. 2,512,717, issued to Dicke, Jun. 27, 1950, there is disclosed power transmission. The focal point of the invention related to power transmissions and particularly to transmissions having infinitely variable drive ratios. The invention comprises a driving friction element and a driven friction element, each of these being frictionally engaged to a rolling member such as a ball and compressed therebetween.
General, in U.S. Pat. No. 3,258,981, issued Jul. 5, 1966, provides a variation on the infinitely variable speed friction drive. In the document, there is a discussion concerning circumferentially spaced rolling friction elements, an example of which is given a steel balls which are used to frictionally transmit a drive between a power input and output race members. In greater detail, the arrangement provided hydrodynamic ball reaction members for the transmission. The reaction ball was supported in a courier having a mating conforming seat supplied with a fluid under pressure to lubricate the ball, but also to provide flotation and reduce frictional losses.
In U.S. Pat. No. 3,272,025, issued Sep. 13, 1966, to Stieber, there is disclosed an infinitely variable speed power transmission which is particularly directed to a ball friction transmission. In the document, power transmission between an input and an output shaft is provided by one ball, which is indicated to be displaceable between two conical surface discs at the end of the two shafts. The same is clamped therebetween by a force, the magnitude of which is variable in conformity with the torque derived therefrom.
Further developments in transmissions were promulgated by Brany. The document is U.S. Pat. No. 3,398,592, issued on Aug. 27, 1968, for an arrangement for the control of the movement of balls.
In U.S. Pat. No. 6,482,121, issued Nov. 19, 2002, to Okoshi, there is disclosed a drive arrangement which clamps an output disc such as a tire with two driving rollers so as to drive the output disc. The drive arrangement is compact, light-weight, low-noise and inexpensive and can be used for a bicycle equipped with an electrical assist drive or various kinds of welfare-specific vehicles. The drive apparatus includes an input shaft and two output shafts extending in a single plane in parallel to each other. The input shaft has an input roller and each of the output shafts has an output roller. A loading roller is located between the input roller and one of the output rollers and an axis of the loading roller is slightly spaced from the plane of the two out shafts. An outer peripheral surface of each roller is a substantially cylindrical rolling surface. The loading roller is preloaded by a preload spring such that it squeezes between the input roller and one of the output rollers. A friction force generated on the rolling surface by a torque exerted on the input roller pushes in the loading roller between the rolling surfaces of the input roller and one of the output rollers so that a large normal force is produced between the rolling surfaces. A friction force at the rolling surface transmits the torque of the input shaft to the two output shafts.
In U.S. Pat. No. 5,697,863, issued Dec. 16, 1997, to Daniel J. Dawe and Charles E. Kraus, there is provided an indefinitely variable traction roller transmission, wherein two toric traction disks are rotatably supported opposite one another and define a torte cavity in which at least two motion transmitting traction rollers are disposed in engagement with the two toric disks and supported by trunnions, the trunnions being pivotally supported to permit changing the ratio of motion transmission between the toric disks. The toric disks each have a different cavity radius, thus causing the circles of contract of the traction rollers with the toric disk to change as the trunnions pivot to various transmission ratio positions, thereby distributing the loads on the traction rollers over a relatively large surface area thus extending the fatigue life of the traction rollers and consequently of the transmission.
In U.S. Pat. No. 5,464,086, issued Nov. 7, 1995, to Axel Coelin, a ball deck is disclosed capable of conveying a container having an uneven button surface. The ball deck, having an upper surface, houses a plurality of ball transfer units. Each ball transfer unit has a first housing having an upper end terminating adjacent the upper surface of the ball deck. A first load supporting ball, which is preferably hollow, is disposed in an upper section of the housing and has a portion extending above the upper surface of the ball deck. A second load supporting ball, having a lesser diameter than the first ball, supports the first ball. A spring biases the balls axially upward by allowing the first ball to move between an upward position and a downward position when supporting an irregular load surface.
In U.S. Pat. No. 4,424,919, issued Jan. 6, 1981, to Ulrich Menzi, there is provided a variable speed transmission of the friction-drive type comprising a driving shaft having at least two ball-driving elements, the driving shaft having drive means associated therewith for rotation of the ball-driving elements. A first torque transmitting means connected with the driving shaft and associated with the ball driving elements rotating the latter in unison with the drive shaft. A first ball means comprising first cage means and at least two balls each of which balls is in rolling contact with the ball-driving element. A drive-shaft provided compromises at least three driven shafts disposed parallel to one another. A second ball means comprises second cage means and at least two balls, each of which balls is in rolling contact with two of the three driven shafts. A gap between the two adjacent ones of the three driven shafts is smaller than the diameter of the respective ball being in contact with these two adjacent drive shafts.
In U.S. Pat. No. 4,224,840, issued Sep. 30, 1980, to Charles E. Kraus, a traction roller transmission is disclosed. The transmission includes coaxial input and output shafts with a sun roller associated with one and a traction ring surrounding the sun roller associated with the other shaft and traction transmitting roller casters disposed in the annular space between and in engagement with the sun roller and the traction ring for the transmission of motion therebetween. Each roller caster includes two transmission rollers whose combined diameters are slightly larger than the gap between the sun roller and the traction ring, one of the transmission rollers being in engagement with the sun roller and the other with the traction ring such that a torque transmitted through the transmission tends to pivot the casters, which are slightly tilted, into a more upright position with respect to the sun roller and traction ring surfaces, thereby forcing the transmission rollers into firm engagement with each other and with the traction ring and the sun roller. The casters have a pivotal support disposed in front of them, with respect to their direction of movement relative to the traction ring and sun roller which both rotate in the same direction, so that the casters swing into perfect parallel alignment with the axis of the sun roller and the traction ring.
In U.S. Pat. No. 6,849,025, issued Feb. 1, 2005, to Kazuo Chikraishi, Atsushhi Maeda and Manabu Abe, a frictional roller transmission is provided. The arrangement comprises a first roller and a second roller disposed around two shafts which are separated from each other in such a manner that the two rollers are not brought into contact, a third roller and a fourth roller which are brought into contact with both the first and second rollers and are disposed between the first roller and the second roller and on an opposite side over a line connecting the center of the first roller and that of the second roller. An angle made by a tangential line between the first roller and the third roller (or the fourth roller) and a tangential line between the second roller and the third roller (or the fourth roller) is set at two times as large an angle of friction obtained from a coefficient of friction between the respective rollers or smaller.
In U.S. Pat. No. 4,011,765, issued Mar. 15, 1977, to Heinrich Tippman, there is disclosed a ball and cone type variable ratio mechanical transmission in which the cone angles are chosen to provide optimum efficiency, increased power handling capability and extended service life.
In U.S. Pat. No. 3,482,461, issued Dec. 9, 1969, to William S. Rouverol, a transmission of the type wherein power is transmitted between a pair of opposed disks by a roller interposed between the disks and mounted on an axis of rotation slantingly disposed relative to the disks. The traction force between the roller and the disks is established by resiliently clamping the roller between the disks.
In U.S. Pat. No. 3,424,018, issued Jan. 28, 1969, to Richard E. Alsch, there is provided a variable transmission having symmetrical discs each with oppositely facing planar faces and held in engagement with transmission balls by face-to-face engagement with input and output members. A holding force is exerted on the drive elements in a pure axial sense and axial thrust bearings provide the medium through which that force is applied with the biasing spring directly engaging the thrust bearing. Friction material provides the drive connection to the input disc and the drive member for the input disc extends through a clearance opening in the housing for connection to an external drive. The ball assembly is supported for pivotal movement about a horizontal axis and the balls provide both the medium of transmission between the discs and the bearing between the cage and its saddle. The bearing surfaces of the ball assembly are coated with a material having a low coefficient of friction.
The entire disclosures of all references recited above are incorporated hereon by reference.